How does king establish his credibility, his ethos in this letter

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https://reflectionsonkosovo.wordpress.com/2012/06/01/ethos-logos-and-pathos-in-kings-letter-from-birmingham-jail/

Examples of Ethos:

1. But since I feel that you are men of genuine good will and that your criticisms are sincerely set forth, I want to try to answer your statement in what I hope will be patient and reasonable terms.

2.You may well ask: “Why direct action? Why sit ins, marches and so forth? Isn’t negotiation a better path?” You are quite right in calling for negotiation.

3.One may well ask: “How can you advocate breaking some laws and obeying others?” The answer lies in the fact that there are two types of laws: just and unjust.